A panorama of the east face of hills showing strata from the John Day Formation in the Painted Hills Unit of the John Day Fossil Beds National Monument, in the U.S. state of Oregon. The strata, which vary in age from 18 million to 39 million years, were formed mainly from ashfalls from volcanoes to the west. The sediment layers vary in their chemical composition and color owing to the ash and other debris falling during varied climatic and volcanic conditions. (click here to see large format)
These beautiful Australian opal nuts consist veins of precious glowing opal within nodules of siliceous ironstone that often form amazing patterns. They vary from 0.5 to 20 cm across, and occur in an iron rich sandstone, near the border with an adjoining mudstone. This one has been sliced and polished into cabochons, revealing the intricacy of the patterns of the gemmy silica within.